The reason I asked the question was that after removing the engine cover (W210), I saw six wires on top of the engine, three go into the engine, the other three go into some types of connectors then feeds into the engine. I was confused by these 3 connectors, since I've never seen this on other makes of cars before.
Thanks for your replies.
P.S. Benzmac, I will take it to a shop for service, but I just wanted to know how the job is done.